ModMaster Manual v3.11 - 2.3.1. Types of address
In this documentation, we use the term "message address" to refer to the address that is actually sent in a message. We use the term "model address" to refer to the address that you supply when you define a register in ModMaster (see Defining registers).
Note that message addresses are restricted to the range 0..65535 since they are transmitted in a 16-bit field in Modbus messages, whereas model addesses are only used internally by ModMaster and may be in the range 0..2147483647.